A pressure measuring device can have a housing and a cylindrical pressure chamber extending from a base freely through the housing. A portion of a pressure chamber wall running parallel to the chamber axis is deformed elastically depending on the internal pressure in the chamber and the resulting deformation is detected by an analyzer or a computer as a measure of the pressure change by a measuring unit coupled with the pressure chamber wall.
Pressure measuring devices whose pressure sensors operate either mechanically, electromechanically or electronically with circuit contacts and/or without contacts are used to measure the static pressure of a fluid. Particularly when a high measurement accuracy is required and the data is needed for further processing in control or data acquisition, electromagnetic pressure sensors operating without contacts are used.
A pressure measuring device operating according to the strain-gauge principle is described in German Open Patent Application No. 26 00 925. This has a measuring tube whose inner space is acted on with a fluid whose pressure is to be measured. Strain gauge strips are cemented on the outside of the measuring tube and connected to a computer or analyzing device.
According to the applied pressure in the measuring tube, the tube together with the strain-gauge strips stretch to a greater or lesser extent. The resistance of the strain-gauge strips acts as a measuring signal.
This pressure measuring device operates very accurately but is very expensive since for one thing, considerable calibration effort and expense is required for balancing the strain-gauge strip bridge circuit to compensate the measuring sensor for temperature changes of the fluid whose pressure is being measured. For another thing, additional and expensive signal amplification for processing the measured signal is necessary.
A pressure measuring device described in German Open Patent Application No. 32 27 516 has a diaphragm displaceable by an applied pressure on which a permanent magnet is positioned. A magnetoresistive sensor is mounted on a housing opposite the permanent magnet. This pressure sensor is of course comparatively simple in structure but has the disadvantage that fluctuations of the surrounding temperature or the temperature of the medium to be measured influence the measurement results. The measurement precision of the pressure sensor is greatly limited.
A pressure measuring device as described in German Open Patent Application No. 29 54 227 has a folding bellows as a pressure sensor whose one end is attached to a coil core which is inserted into an electromagnetic coil to a depth which varies according to the expansion of the folding bellows.
The coil and folding bellows are mounted in a supporting plate.
The supporting plate, folding bellows, coil core and coil body in this device are made with materials chosen so that on varying the ambient temperature the thermal expansions of the individual components compensate each other. In this way this pressure measuring device operates independently of the ambient temperature with a constant precision.
Disadvantageously, however, the cost of the device is considerable, particularly because of the materials which must be used.
A pressure measuring unit for measurement of a high pressure according to the principles of this device is made only with difficulty and with unacceptably large costs. Another disadvantage is that the temperature compensation mechanism operates only for variations of the ambient temperature but not for variations of the temperature of the medium to be measured.